Question: Expand.
Solution: $\begin{aligned} &\phantom{=}({y^2-9})(y^2-4) \\\\ &={y^2}(y^2-4){-9}(y^2-4) \end{aligned}$ $\begin{aligned} &=y^4-4y^2-9y^2+36 \\\\ &=y^4-13y^2+36 \end{aligned}$